In the original version of TNG: "Darmok", the forward torpedo launcher of the Galaxy-classUSS Enterprise-D was depicted as having an integrated phaser bank as well. The effect was however replaced in the remastered release of the episode with the phaser blasts coming from the saucer section phaser array.

The Star Trek: The Next Generation Technical Manual suggests that the launcher systems of the 24th century combines something similar to a light gas gun and a mass driver, as there is gas pressure chamber with launch-assist gas generators and an electromagnetic accelerator. The launcher tube is also strung with sequential field induction coils. They give a hand-off warp field to the probes and torpedoes that are powered by internal warp sustainer engines. This allows the torpedo to achieve a faster warp speed than the ship when traveling at warp. The Galaxy-class starship launchers can fire up to 10 torpedoes simultaneously from a single launchtube. (pg. 118 diagram, 129, 130)

It is stated in the Star Trek: Deep Space Nine Technical Manual that some of the smaller Starfleet craft such as shuttles, (pg. 143) runabouts (pg 149) and even the Deep Space 9's weapon sail towers (pg. 82, 83) utilize microtorpedo launchers. They are simple delivery systems, without magnetic accelerators, as microtorpedoes use a miniature fusion thruster for propulsion. Even a micro-quantum torpedo launcher is depicted on page 149.

According to Rick Sternbach there actually is a distinct microtorpedo launcher on the runabout model. [1]

Even though the script and dialogue called for only standard torpedoes, according to John Eaves, on the VFX teams suggestion, powerful microtorpedo launchers were indeed added to the rotary weapon arrays on DS9. The model and effects seem to confirm six round torpedo tubes on each rotary array. Extremely small compared to the larger regular torpedo tubes on the other weapon arrays. [2]